Most commercial photo-quality inkjet media can be classified in one of two categories according to whether the principal component material forms a layer that is porous or non-porous in nature. Inkjet media having a porous layer are typically formed of inorganic materials with a polymeric binder. When ink is applied to the medium it is absorbed quickly into the porous layer by capillary action. However, the open nature of the layer can contribute to instability of printed images. Inkjet media having a non-porous layer are typically formed by the coating of one or more polymeric layers onto a support. When ink is applied to such media, the polymeric layers swell and absorb the applied ink. However, due to limitations of the swelling mechanism, this type of media is slow to absorb the ink, but once dry, printed images are often stable when subjected to light and ozone.
A method of manufacturing a material that addresses these problems is required. The applicant has recognised that use of a polymer foam coated on a support would address the problems associated with the inkjet media. A method of manufacturing such a material is required. Although the material when manufactured would be useful as an inkjet media, its use would not be limited in this regard. Indeed, the material may find uses in any number of applications. For example, the material may be used as insulation tape, a coating for e.g. shelves, sticky-backed coating material, and any other possible use for a material.
Traditionally, polymer foams are manufactured using mostly hydrophobic thermoplastic materials such as Polyurethane, Polyvinyl Chloride (PVC) and Polyethylene, which require high processing temperatures. Initially, a gas-filled polymer is formed from which the polymer foam is formed. One example of a typical method of forming a gas-filled polymer relies on the thermal decomposition of chemical blowing agents within a polymer solution, thereby generating nitrogen N2 or carbon dioxide CO2 gas in the solution. The thermal decomposition may be caused by the application of heat or as a result of the exothermic heat of reaction during polymerisation.
An alternative method of creating a gas-filled polymer involves the mechanical whipping of gases into a polymer melt, which then hardens either by catalytic action or heat, trapping gas bubbles in a matrix. Low boiling point liquids LBPLs may also be used. Volatilisation of LBPLs e.g. methylene chloride within the polymer melt occurs as a result of the application of heat or the exothermic heat of reaction. Accordingly, gas is introduced into the polymer forming a gas-filled polymer. In one example, gas dissolved in a polymer expands upon reduction of pressure in the system, thereby causing the formation of gas bubbles in the polymer. Alternatively, microspheres may be incorporated into a polymer mass, the spheres consisting of gas-filled polymer that expands upon heating.
In all these cases, after obtaining the gas-filled polymer, typically a foam is then formed using one of three common manufacturing processes: compression moulding, reaction injection moulding or extrusion of the foam.
A problem with these processes is that the temperatures involved can be very high, e.g. in excess of 150° C., as the polymers used are in their molten state. The most common processing method used in creating polymer foam films is extrusion. This is a three stage operation consisting as a first stage of forming a polymer solution with gas dissolved in it. This may be achieved by injection of N2 or CO2 into the solution or by the use of blowing agent, to create a single phase solution. Next, nucleation sites are formed, as a result of a rapid pressure drop to create large numbers of uniform sites. Finally, cell growth then takes place by means of diffusion of the gas to form bubbles. Control of cell growth is achieved by controlling processing conditions such as pressure and temperature.
Methods of forming porous polymer layers have been disclosed such as those disclosed in U.S. Pat. No. 6,228,476 and U.S. Patent Application Serial No. 2001/0021726. Such methods rely on the use of curable polymers.
U.S. Pat. No. 3,794,548 discloses the use of polyurethane in a porous polymer film. Heating of the polymer causes volatilisation of solvents within the polymer resulting in a porous coating.
A method of forming a foamed polymer material is required that uses very low processing temperatures in comparison to all traditional methods.